1. Field of the Invention
The present invention relates to a semiconductor optical amplifier type gate switch drive circuit, a semiconductor optical amplifier type gate switching device, and an optical cross connect. In particular, the present invention relates to driving of the semiconductor optical amplifier type gate switching device.
2. Description of the Related Art
In recent years, in order to promote multi-media networks, there has been an urgent demand for developing speedy and larger capacity optical communication devices. As one approach to realize such optical communication devices, research and development are being made on ultra-high speed optical switches with switching time of nanosecond order. A semiconductor optical amplifier (SOA) type optical gate switching device is an example of such an ultra high speed optical switching device. The SOA type optical gate switching device is switched between ON and OFF based on a drive current output by a drive circuit. An operational amplifier that is capable of amplifying signals output from a signal generator is built in the drive circuit that outputs the drive current. A conventional technology has been disclosed in Japanese Patent Application Laid-open No. 2001-154160. Conventional operational amplifiers built in the drive circuit consists of a high-speed operational amplifier that is operable at 100 MHz of bandwidth, 1000 V per microsecond of the through-rate, 300 mA of the output (drive) current capacitance, and at 20 nanoseconds of the settling time.
Japanese Utility Model No. 2508175 discloses a parallel output synthesizing circuit that supplies electric power to an electric load comprising a large electric power by linking a plurality of amplifiers in parallel with each other.
To enhance the efficiency for transmission of optical packet signals, a still faster driving capability is demanded for the SOA type optical gate switching devices. Nevertheless, due to the conventional performance capability currently provided for any of conventional SOA type high-speed operational amplifiers, none of them has so far been able to satisfy the urgently demanded faster driving performance. Hence, as an alternative, it is one may think of using an SOA type operational amplifier capable of operating itself with a higher performance capability rated at 5000 V per microsecond and 150 mA of the output current capacitance operable at 1 GHz of bandwidth. However, when such a faster operational amplifier is used in an optical switching device, it is quite difficult for the optical switching device to satisfy 300 mA of the output current (drive current) capacitance currently being demanded.
To enhance the output current capacitance, taking a hint from Japanese Utility Model No. 2508175, one may think of connecting a plurality of operational amplifiers in parallel with each other. However, Japanese Utility Model No. 2508175 merely describes a method of supplying an increased amount of current to load in the parallel output synthesizing circuit as the main pursuing object without caring about the method of driving load at an increased rate at all.